They didn't actually fire the board of the non-profit. They just said they'd all quit in protest because of an action of the board they all felt was egregious. The board could have stayed and been a non-profit that did nothing ever again. They decided it was better to step down.
>>cma+H6
I believe it was Helen Toner who claimed an OpenAI lawyer said they were at risk of breaching fiduciary duty if the company fell apart because of the ouster.